Generally, the identification of the type and authenticity of the sheet paper of bank notes, checks or gift certificates or the like employs a magnetic sensor or light sensor and is performed by magnetically or optically extracting the characteristics of sheet paper that is inserted by the user.
The extraction of the optical characteristics of sheet paper using a light sensor acquires an image pattern of the sheet paper by acquiring an image pattern by extracting the design, dimensions and orientation and so forth of sheet paper by using a transmission-type or reflective type light sensor, and identifies the type and authenticity of the inserted sheet paper by comparing the acquired image pattern with a standard pattern of a genuine bill for each type.
Here, in order to reduce the effects of noise caused by dirt or the like attached to the sheet paper, there are counterfeit bill identification devices or the like that identify whether a bill is genuine or counterfeit by reading a transparent pattern of a bill by means of two optical reading means that utilize transmitted light and reflected light and comparing both data sets thus read, as disclosed in Japanese Patent Application Laid Open No. 2002-92683, for example.
Further, as disclosed in Japanese Patent Application Laid Open No. H6-203244, there are counterfeit medium discrimination devices that discriminate between genuine and counterfeit media by reading an image of a medium by means of a CCD sensor by using transmitted light, extracting a pattern of a transparent area of the medium from the image thus read, and removing the effects of nonlinear blurring of the extracted pattern data.
However, in the conventional technologies cited above, even when dust is attached to the interior of an image pickup section, the existence of the dust is not identified and identification based on the picked up sheet-paper image is performed. Therefore, there is the inconvenience that erroneous identification or the like caused by dust arises and the sheet paper identification device is used while identification is not performed correctly and acceptance of the sheet paper is no longer possible instead of the abnormal state in the image pickup section caused by dust being communicated to the outside.